Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
  • H03H9/02—Details
  • H03H9/125—Driving means, e.g. electrodes, coils
  • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
  • H03H9/02—Details
  • H03H9/125—Driving means, e.g. electrodes, coils
  • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
  • H03H9/14502—Surface acoustic wave [SAW] transducers for a particular purpose
  • H03H9/14505—Unidirectional SAW transducers
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
  • H03H9/02—Details
  • H03H9/125—Driving means, e.g. electrodes, coils
  • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
  • H03H9/14517—Means for weighting
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
  • H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
  • H03H9/02—Details
  • H03H9/125—Driving means, e.g. electrodes, coils
  • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
  • H03H9/14517—Means for weighting
  • H03H9/14523—Capacitive tap weighted transducers

Definitions

• the invention relates to an interdigital transducer for generating surface acoustic waves, in short surface wave transducers or in the following also generally called transducers.
• a transducer usually consists of two comb-shaped electrodes, each called a current busbar or busbar and comprising electrode fingers attached to it. Two such interdigitated electrode combs form an interdigital transducer.
• a surface wave filter can be constructed, for example, from a piezoelectric substrate with two interdigital transducers serving as input and output transducers. The acoustic generated in the input converter
• the path of the surface acoustic wave which may be limited on both sides of the transducers by reflectors or may extend into them, is also referred to as the acoustic track.
• the efficiency of the electro-acoustic conversion is optimal at the center frequency.
• the filter is set so that it has good pass behavior over a desired bandwidth in the vicinity of its center frequency. Within this band, a filter should have the lowest possible insertion loss, that is to say a low loss in the coupling and transmission of the surface wave. Signals outside this band should be attenuated in the filter.
• a narrow band filter can be obtained by increasing the number of electrode fingers so that a long transducer is obtained.
• each electrode finger of the normal finger transducer is replaced by two split fingers arranged at a distance of ⁇ / 4, which are mechanically reflection-free, since the reflections of the two fingers cancel each other out.
• problems can also arise here in the case of longer transducers, so that a split transducer transducer is not free of reflection due to the electrical regeneration at the non-zero terminating impedance at the acoustic gates
• a reflective electrode finger is arranged in a unit line of length ⁇ st, over whose width and exact position the reflection of this cell can be adjusted. In this way it is possible to model a transducer that has a desired reflection distributed across the transducer. This distributed reflection can follow a weighting, for example.
• a transducer according to the invention is made up of a number of basic cells arranged in a row in the direction of propagation of the surface wave, all of which have the approximate length ⁇ , where ⁇ represents the center frequency of the transducer.
• the transducer can be divided into stimulating and reflecting base cells to which the reflection contribution has only certain values mx R 0 , where m can take the values -2, -1, 0, 1 or 2, and where R 0 is a reference reflection.
• Each of 0 different reflection contributions has the same phase position ⁇ O.
• the phase position and excitation strength like the number of stimulating fingers, are identical in all stimulating basic cells.
• the phase relationship between excitation and reflection leads to the unidirectional behavior of the transducer, with phase alignment being obtained in one preferred direction, but phase opposition in the opposite direction.
• a transducer according to the invention is no longer subdivided strictly into stimulating and reflecting fingers; rather, stimulating fingers also have a contribution to reflection which is optimized to the desired phase position and strength by varying the finger width and finger position. This can also increase the unidirectionality of the converter, which in a filter with such a converter leads to reduced insertion loss, a longer impulse response and steeper flanks of the passband of the pass curve.
• the stimulating base cells of a transducer according to the invention can all have exactly one electrode finger individually connected to a busbar as a stimulating electrode.
• a transducer in which the finger widths and spacings of the electrode fingers increase or decrease continuously in the transverse direction (transverse to the direction of propagation of the surface wave). Such a measure increases the bandwidth of a converter and thus also the bandwidth of a filter in which the converter according to the invention is used.
• the transducer is designed to focus and has electrode fingers with curved edges.
• Such a transducer has the advantage that, when used as an input transducer in a surface acoustic wave filter, the scattering losses are reduced, since the focusing also means that those surface waves still get into the receiving and output transducers that can no longer reach the input transducer with electrode fingers that are running would. This also lowers the insertion loss of the converter or filter.
• all finger widths and all finger spacings of the electrode fingers are different in each basic cell. This means that a certain finger width or a certain finger distance occurs at most once within a basic cell.
• this is preferably, but not exclusively, used in an IF filter which, with the invention, has a low insertion loss and, due to the additionally created resonance spaces, an extended impulse response.
• FIGS. 2a to c show different types of double finger cells
• FIG. 3 shows an exemplary basic cell according to the invention
• the precise determination of the finger geometries, in particular the finger widths and the finger distances, is carried out by formulating a solvable optimization task.
• Optimization methods for transducers are already known, but these are subject to restrictions, so that the cells to be constructed have fewer degrees of freedom than the geometry widths available.
• the problem can be generalized for an optimization method for producing transducers according to the invention, so that the restrictions applicable to previous optimization methods, in particular the fixed relationships of finger widths and positions, are eliminated.
• the reflection of a cell could only be adjusted by the metallization height.
• a continuous width variation of the reflection finger or fingers is now possible.
• the geometries without excitation are formed directly from the geometries with excitation by omitting the overlap, for example by changing the finger connection sequence.
• the basic cells from known single and double finger cells are selected as the starting geometries for the optimization task.
• Figures la to c show three different approaches for single finger cells, in which only one electrode finger is arranged on the signal-carrying busbar.
• the Single finger cells can be composed of three or four electrode fingers.
• FIG. 1 a shows a single-use cell without reflection that can be used as a starting point and has a regular ⁇ / 8 finger arrangement in the ⁇ / 8 grid, which is reflection-free in the event of an electrical short circuit.
• FIG. 1c shows how a single finger cell with negative reflection is created from this cell by exchanging two electrode fingers.
• the phase difference of the reflection between cells with positive and cells with negative reflection is 90 °, so that the phase difference of the reflection at the transducer ends of these simple transducers is 180 °.
• FIGS. 2a to c show different types of double finger cells, in each of which two electrode fingers are connected to the signal-carrying busbar.
• FIG. 2a again shows a regular ⁇ / 8 finger arrangement that is reflection-free.
• FIG. 2b shows a double finger cell with positive reflection
• Figure 2c shows a double finger cell with negative reflection.
• the known and known single and double cell cells serve as the starting point for the optimization. If a converter is electrically connected, i.e. connected to an external load, acoustic-electrical feedback M iV) 1

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• Physics & Mathematics (AREA)
• Acoustics & Sound (AREA)
• Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=7633184

Family Applications (1)

Country Status (8)

Families Citing this family (16)

Citations (4)

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• 2000
  • 2000-03-02 DE DE10010089A patent/DE10010089A1/de not_active Ceased
• 2001
  • 2001-02-19 KR KR1020027011393A patent/KR100752828B1/ko active IP Right Grant
  • 2001-02-19 CA CA002400719A patent/CA2400719A1/en not_active Abandoned
  • 2001-02-19 CN CNB018058949A patent/CN1190893C/zh not_active Expired - Lifetime
  • 2001-02-19 US US10/204,103 patent/US6777855B2/en not_active Expired - Lifetime
  • 2001-02-19 EP EP01913681A patent/EP1264397A1/de not_active Withdrawn
  • 2001-02-19 WO PCT/DE2001/000630 patent/WO2001065688A1/de not_active Application Discontinuation
  • 2001-02-19 JP JP2001564458A patent/JP2003526240A/ja not_active Withdrawn

Patent Citations (4)

Non-Patent Citations (2)

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